1. Field Of The Invention
The present invention relates to barriers for hearing aids. More particularly, the present invention relates to a disposable membrane cerumen and moisture barrier with a low acoustic impedance.
2. The Prior Art
With the vast improvement in integrated circuit technologies and signal processing capabilities in recent years, the focus of hearing aid technologies has shifted from a behind-the-ear hearing aid resting on the visible external ear to an in-the-ear hearing aid that is inserted almost entirely into the ear canal. In a typical in-the-ear hearing aid, a microphone disposed within the hearing aid shell and adjacent to an input sound port receives an acoustic signal and transduces the acoustic signal into an electrical signal. The electrical signal is processed, and the processed signal is output to an electro-acoustic output transducer that converts the processed electrical signal to an acoustic signal. A sound passage tube connected to the output transducer passes the acoustic signal through a sound outlet port in the tip of the hearing aid shell. The sound outlet port is usually proximal to the ear drum of the hearing aid user, and is positioned approximately mid-canal.
An ear canal into which an in-the-ear hearing aid is disposed has a bent shape and consists essentially of two portions. The first portion is closest to the external ear and extends typically a little over a centimeter into the ear canal, has soft tissue between the skin and the underlying bone to form a padded area, and has tiny hairlike projections. Cerumen or wax is produced in this portion of the ear canal. The second portion is closest to the ear drum and comprises skin over bone, with little soft tissue to offer padding between the skin and bone. Because of the lack of padding in the second portion, the skin in the second portion is quite sensitive to any foreign body that is placed against it. As such, in-the-ear hearing aids are typically placed such that the portion of the hearing aid pressing against the hearing canal does not extend further than the first portion of the ear canal.
Unfortunately, the cerumen which is produced in the first portion of the ear canal can then more readily cause problems with the operation of the hearing aid. There are at least two problems well known to those of ordinary skill in the art that cerumen can cause. First, is a clogging of the outlet sound port which reduces sound transmission from the hearing aid to the hearing aid user. Second is cerumen travelling down the sound tube to impair, disable or ruin the electro-acoustic transducer. As a result, a wide variety of apparatus have been proposed in the prior art that act as a barrier between the cerumen and the sound tube.
In the examples of the various cerumen barriers given below, the ease of cleaning and replacement, frequency of cleaning and replacement, and acoustic attenuation are just a few of the design issues that were contemplated. The various cerumen barriers include complex mechanical arrangements that form a difficult or tortuous path for cerumen to travel along to get to the sound outlet port, a filter, a torturous path in combination with a filter, grooves or areas in the barrier designed to collect cerumen, etc.
As examples of a tortuous path cerumen barrier, U.S. Pat. No. 4,870,689 describes a housing that is positioned within the tip of the hearing aid and has a plurality of projections within the substantially cylindrical housing to impede and accumulate cerumen entering the housing, and U.S. Pat. No. 5,105,904 describes the combination of a component and a cap, wherein the component is insertable into the tip of a hearing aid and has a number of circumferentially spaced angle brackets and radially projecting bracket locking detents and a cap that fits over the angle brackets and onto the locking detents.
As an example of a filter, U.S. Pat. No. 5,401,920 describes a cerumen barrier which comprises a thin flexible membrane one surface of which has a pressure sensitive adhesive layer so that the membrane may be affixed to the tip of the hearing aid. And as examples of a tortuous path combined with a filter U.S. Pat. No. 4,553,627 describes a cerumen barrier having a stem portion and a head portion, wherein the stem portion is inserted into the tip of the hearing aid and has an axial tube with an acoustic filter disposed therein and which communicates with a cross passage which extends through the head portion, and U.S. Pat. No. 4,972,488 describes a housing that is positioned within the tip of the hearing aid and has a plurality of projections within the substantially cylindrical housing to impede and accumulate cerumen entering the housing, and a screen to further impede and accumulate cerumen.
As examples of cerumen barriers that have specific places designed to accumulate cerumen, U.S. Pat. No. 4,953,215 describes a non-porous membrane which covers an electro-acoustics transducer which projects into a sound conducting channel, wherein the non-porous membrane has a bore that communicates with the channel, and U.S. Pat. No. 4,879,750 discloses a perforated cap which is secured to a protrusion on the tip of the hearing aid and has a substantially flat end plate adjacent to the protrusion which bears a groove for collecting cerumen.
As further examples of cerumen barriers, U.S. Pat. No. 4,945,569 describes a tube section which projects beyond the tip of the hearing aid and further has a yoke formed over the tube of the tube extending from the tip of the hearing aid. U.S. Pat. No. 5,099,947 describes a cerumen guard which is formed as a coil of wire cone that is interference fitted into the receiver of a hearing aid. U.S. Pat. No. 5,278,360 describes a cerumen trap which has a body that is inserted into and affixed to the tip of a hearing aid shell and which communicates with the sound tube and a bridge that is formed integrally with the body and extending over the opening in the body, wherein the bridge includes both a bar and a shielding member. U.S. Pat. No. 5,293,008 discloses a cerumen trap which includes a piston or plug shaped member for pushing cerumen out of the cerumen trap. And U.S. Pat. No. 5,327,500 describes a sound outlet base and a barrier door, wherein the sound outlet base is inserted and secured into the sound outlet port of the hearing aid shell and the barrier door is inserted into the counterbore of the sound outlet base.
Though each of these cerumen barrier designs to some degree address one or all of the design issues set forth above and other design issues as well, their exists the need for a cerumen barrier that prevents cerumen and moisture from entering the sound outlet passage, may be easily replaced, and provides a desired acoustic response.